Gas turbine engines are typically configured for maximum efficiency at a single operating condition or design point. Engines for a civil or military transport aircraft are optimized for subsonic cruise conditions. Engines for a supersonic transport or strike aircraft are optimized for supersonic dash conditions. Operation of the gas turbine at any condition away from the design point seriously compromises performance as cycle parameters such as bypass ratio and pressure ratio are non-optimum. Additionally, fan diameter and core size can be set by takeoff thrust requirements or single engine out conditions. The gas turbine engine can thus be oversized for the design point condition. As a result, fuel burn is compromised at both the design and off design conditions.
It is desirable to have a gas turbine engine which can adapt to a variety of flight conditions and provide desired performance. Accordingly, there remains a need for further contributions in this area of technology.